Double sided scrubbers clean the top and the bottom of a wafer simultaneously. Double sided scrubbers are usually automated and comprise a conveyor type mechanism, rollers, and brushes. In general, the wafer lies flat on the conveyor mechanism and the conveyor mechanism moves the wafer into the brushes. While being scrubbed, the wafer is supported (or held horizontally) by the conveyor mechanism, brushes, rollers, or a combination thereof.
FIG. 1 is a general view of a conventional double sided wafer processing station. Wafer 10 is processed by brushes, one of which is shown as brush 20 and the other (not shown in FIG. 1) is beneath wafer 10 and directly below brush 20. Rollers 30 rotate wafer 10 so the entire wafer surface may be processed. Each of brushes 20 is rotated about its central axis by motor 40. The rotary motion of roller 30 is then transferred to wafer 10 when the edge of each roller 30 comes into contact with the outer edge of wafer 10.
Brush cleaning systems can effectively process the top and bottom of semiconductor substrates. However, brushes do not provide a sufficient amount of mechanical energy at the edge/bevel to remove contamination. In other words, although the double sided scrubber of FIG. 1 is effective at cleaning the front and back side of a wafer, it can leave a residue on the edge/bevel of the wafer.
One solution to cleaning the edge/based areas is shown in U.S. Pat. No. 5,861,066, entitled "Method and Apparatus for Cleaning Edges of Contaminated Substrates", issued Jan. 19, 1999 in which the edge and/or based areas may be cleaned using rollers that contact the outer edge of a wafer, similar to roller 30 coming into contact with wafer 10 above, except that one of the rollers includes an abrasive area and rotates such that the tangential velocity at the point of contact between the one roller and the wafer is different than the speed at which the other roller rotates the wafer. It is because of this difference in speed that the edge/bevel area is cleaned by the abrasive area.